PO175 system too rich (bank2) and PO171 system too lean (bank1). These were fault codes for a 2003 f150. It did not pass state inspection due to this. They tested the o2 sensors and said they were good and the next step would be process of elimination replacing parts until it cleared inspection. I thought if you had fault codes that would lead you to the problem. I don't have an open check book to just start replacing stuff to eliminate it. I'd really like to replace the item that causes the fault. Any help?

 

Upperor lower O2 sensors tested?? There are usually 4 O2 sensors on V-6, V-8, V-10 engines.One in each manifold andafter each cat.You could have problems with the lower ones. If they all check out fine checkthe fuel pressure in the rail. FYI, most of your sensors can be tested via a digital multimeter, a good repair manual will give you the specs.